Faraday waves in binary non-miscible Bose-Einstein condensates

We show by extensive numerical simulations and analytical variational calculations that elongated binary non-miscible Bose-Einstein condensates subject to periodic modulations of the radial confinement exhibit a Faraday instability similar to that seen in one-component condensates. Considering the hyperfine states of $^{87}$Rb condensates, we show that there are two experimentally relevant stationary state configurations: the one in which the components form a dark-bright symbiotic pair (the ground state of the system), and the one in which the components are segregated (first excited state). For each of these two configurations, we show numerically that far from resonances the Faraday waves excited in the two components are of similar periods, emerge simultaneously, and do not impact the dynamics of the bulk of the condensate. We derive analytically the period of the Faraday waves using a variational treatment of the coupled Gross-Pitaevskii equations combined with a Mathieu-type analysis for the selection mechanism of the excited waves. Finally, we show that for a modulation frequency close to twice that of the radial trapping, the emergent surface waves fade out in favor of a forceful collective mode that turns the two condensate components miscible.Comment: 13 pages, 10 figure

Antibody-dependent cellular cytotoxicity against drug-induced antigens in L5178Y mouse lymphoma.

In vivo treatment with antineoplastic compounds has been reported to lead to the expression of new antigenic specificities which were not detected on parental cells, and which were transmissible as a genetic character. The current study is concerned with antibody-dependent cellular cytotoxic (ADCC) activity in serum of syngeneic mice challenged with LY/DTIC cells, a subline of LY murine lymphoma, antigenically altered by the drug DTIC. LY/DTIC target cells coated with LY/DTIC-immune serum were specifically lysed by virgin lymphocytes. The genetic background of the effector cells, whether syngeneic, allogeneic or xenogeneic, did not produce significant differences in the percentage of target-cell lysis. ADCC activity was reduced when the immune serum was added directly to the incubation medium, without precoating. Although sera from individual animals exhibited different levels of ADCC activity, they nevertheless followed the general trend of the pooled sera. Peak activity of ADCC was obtained in the sera collected on Days 8 and 30 after LY/DTIC cell challenge. The ADCC activity elicited by LY/DTIC cells may contribute to the rejection of drug-altered tumour cells

Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance

We study magnetic-field-dependent nonresonant microwave absorption and dispersion in thin La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films and show that it originates from the colossal magnetoresistance. We develop the model for magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The model accounts fairly well for our experimental findings, as well as for results of other researchers. We demonstrate that nonresonant microwave absorption is a powerful technique that allows contactless measurement of magnetic properties of thin films, including magnetoresistance, anisotropy field and coercive field.Comment: 20 pages, 11 figure

Spatial period-doubling in Bose-Einstein condensates in an optical lattice

We demonstrate that there exist stationary states of Bose-Einstein condensates in an optical lattice that do not satisfy the usual Bloch periodicity condition. Using the discrete model appropriate to the tight-binding limit we determine energy bands for period-doubled states in a one-dimensional lattice. In a complementary approach we calculate the band structure from the Gross-Pitaevskii equation, considering both states of the usual Bloch form and states which have the Bloch form for a period equal to twice that of the optical lattice. We show that the onset of dynamical instability of states of the usual Bloch form coincides with the occurrence of period-doubled states with the same energy. The period-doubled states are shown to be related to periodic trains of solitons.Comment: 4 pages, 3 figures, change of conten

Fractional-Period Excitations in Continuum Periodic Systems

We investigate the generation of fractional-period states in continuum periodic systems. As an example, we consider a Bose-Einstein condensate confined in an optical-lattice potential. We show that when the potential is turned on non-adiabatically, the system explores a number of transient states whose periodicity is a fraction of that of the lattice. We illustrate the origin of fractional-period states analytically by treating them as resonant states of a parametrically forced Duffing oscillator and discuss their transient nature and potential observability.Comment: 10 pages, 6 figures (some with multiple parts); revised version: minor clarifications of a couple points, to appear in Physical Review

Collapse and revival of oscillations in a parametrically excited Bose-Einstein condensate in combined harmonic and optical lattice trap

In this work, we study parametric resonances in an elongated cigar-shaped BEC in a combined harmonic trap and a time dependent optical lattice by using numerical and analytical techniques. We show that there exists a relative competition between the harmonic trap which tries to spatially localize the BEC and the time varying optical lattice which tries to delocalize the BEC. This competition gives rise to parametric resonances (collapse and revival of the oscillations of the BEC width). Parametric resonances disappear when one of the competing factors i.e strength of harmonic trap or the strength of optical lattice dominates. Parametric instabilities (exponential growth of Bogoliubov modes) arise for large variations in the strength of the optical lattice.Comment: 9 pages, 20 figure

Strain and correlation of self-organized Ge_(1-x)Mn_x nanocolumns embedded in Ge (001)

We report on the structural properties of Ge_(1-x)Mn_x layers grown by molecular beam epitaxy. In these layers, nanocolumns with a high Mn content are embedded in an almost-pure Ge matrix. We have used grazing-incidence X-ray scattering, atomic force and transmission electron microscopy to study the structural properties of the columns. We demonstrate how the elastic deformation of the matrix (as calculated using atomistic simulations) around the columns, as well as the average inter-column distance can account for the shape of the diffusion around Bragg peaks.Comment: 9 pages, 7 figure